During a concrete pouring process, a material that includes aggregates, cement, and water is poured into an area that may be bounded by forms to contain the concrete material. As concrete is delivered into the pour area, a plurality of laborers, often called “puddlers,” using tools such as rakes, come-alongs, and/or shovels, distribute the concrete material to generally the desired elevation. Still other laborers, commonly equipped with a piece of lumber or other straight member referred to as a “strike-off,” move the strike-off across the concrete material. The process of manually striking-off the concrete material consolidates the material and forces the larger aggregate below the finished elevation. It also shapes the surfaces of the concrete to the desired slope or “grade.” The levelness of the finished surface is highly dependant on the skill of the personnel handling the strike-offs. Additionally, manually striking-off the concrete material is very labor-intensive and requires a great deal of skill and experience to ensure a flat and properly inclined finished surface.
The advent of the portable vibratory screed greatly reduced the labor associated with leveling of the concrete material. Portable vibratory screeds commonly include a vibration-inducing mechanism attached to a board or “blade” and one or more operator-manipulated handles that extends from the blade. The vibration mechanism typically comprises an “exciter” formed from one or more eccentric weights driven by a motor. Operation of the exciter consolidates the concrete material such that, as the blade is moved across the wet concrete, the vibrating blade forces the larger aggregate below the surface of the material and works a highly cementatious material with smaller aggregates, often called “cream,” to the finish surface of the material. Operator manipulation of the handle, as well as the rigidity of the blade, directly affects the flatness and inclination of the finished surface of the material. Accordingly, an operator's ability to control the pitch or tilt of the blade as well as the speed and direction of travel of the blade determines the flatness of the finished material.
The elevation of the finished material is commonly determined by the operator's visual inspection of the finish elevation in relation to the elevation references such as the forms. More recently, laser-based grade indication systems have been developed that provide precise position information that the operators can use as feedback to manipulate the screed. The typical laser system comprises a reference laser and a laser receiver. The laser is positioned on a tripod or similar support outside of the pour area and emits a laser beam in all directions at a known reference height. The laser receiver is mounted on a vertical post or mast supported on the screed blade at the reference height. The height of the receiver usually can be adjustable by adjusting the length of the mast but is fixed during any particular screeding operation. An indicator on the receiver indicates whether the receiver is level with, above, or below the desired reference plane or “grade” set by the laser transmitter. The operator relies on the grade information provided by the indicator as feedback to maintain the screed at the desired height and inclination.
In order to minimize interference from personnel and other obstructions in and around the pour area, some laser receivers are mounted on masts that extend over the operator's head. However, an operator cannot monitor operation of the working rear or leading edge of the screed blade while simultaneously viewing the receiver's indicator. He or she instead must repeatedly glance up and down so as alternately view the indicator and the leading edge of the screed. This constant glancing up and down can be very fatiguing to the operator. It also increases the chances of operator error.
In addition, the display provided by the typical commercial receiver's indicator is ill-suited for use on a concrete screed equipped a laser elevation/inclination indicator because its generic output only indicates whether the receiver is below or above a reference height. Some receivers do not provide any quantitative information about the magnitude of the offset. The operator therefore must use dead reckoning to determine the magnitude of screed manipulation that is required to obtain the proper height. Other systems attempt to provide an indication of the degree to which the screed is off-grade by flashing an out-of-grade indicator light at a frequency that progressively changes as the screed moves progressively further off-grade. These displays are not intuitive. They also require the operator to view the display for a relatively long period of time to process the information. That is, he or she must view the display sufficiently long to discern the frequency of the flashing display. The delay required for this processing time detracts from the operator's ability to react quickly to an out-of-grade condition and also distracts the operator from monitoring blade operation directly.
The need therefore has arisen to provide a portable vibratory wet concrete screed with a laser indicator whose receiver is relatively immune to interference from obstructions in the vicinity of the screed but whose indicator can be viewed by an operator while simultaneously monitoring operation of the screed blade.
The need also has arisen to provide a wet concrete screed with a laser elevation system that displays easily understandable qualitative and quantitative grade-based information.
Transporting wet concrete screeds having laser elevation systems and/or other portable vibratory wet concrete screeds can also prove a challenge. Screeds occupy “footprints” in both the horizontal and vertical planes defined by rectangular boxes the length, width, and height of which are defined by the maximum length, width, and height of the screed. Both the handles and the receiver masts of a wet concrete screed extend to a height of several feet well above the top of the exciter assembly, typically at least doubling the vertical footprint that would otherwise be occupied by the screed. In addition, the handles extend several feet behind the blade, typically at least tripling the horizontal footprint that would otherwise be occupied by the screed. While screeds have been provided with partially telescoping receiver masts and/or handles that fold approximately midway along their length to facilitate transport, the minimum vertical and horizontal footprints of these screeds are still typically at least double those of the blade and exciter combination. The only way to reduce the footprint of the screed to that of the blade and exciter assembly combination was to disassemble and remove the handles and receiver masts. Disassembling and removing those structures is a time-consuming process that risks loss of components. It also risks assembler error in reassembly.
The need therefore has arisen to provide a wet concrete screed in which the handle(s) and receiver masts (if present) can be folded flat onto the blade so as to reduce the vertical and horizontal footprints of the screed to essentially those provided by the screed and exciter combination.